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Sunday, November 13, 2011

Making silica aerogel at home

I followed instructions in the silica TMOS recipe from http://www.aerogel.org and successfully produced some small pieces of aerogel in my home shop.

The two main difficulties are: 1. Getting TMOS or TEOS (the key chemical ingredient), and 2. Building a supercritical drying chamber. The components for the chamber can be bought from http://www.mcmaster.com or another source of industrial pipe fittings. You'll also need a supply of liquid carbon dioxide. I used a 20-lbs cylinder, which I bought from a local welding store. Most of the cost is in the cylinder itself, since a refill costs only $20 to $30. You may find a welding supply shop that will rent the cylinder.

Getting the TMOS is difficult since chemical suppliers are generally unwilling to sell to individuals.

The process to make aerogel is:

1. Mix TMOS, methanol, and ammonium hydroxide. Pour this mixture into molds, and wait for a gel to form.2. Submerge the gel in methanol, and wait a day for the remaining water in the gel to diffuse into the methanol.3. Discard the methanol, and replace with fresh methanol. Wait a day, and repeat. Repeat this process a few times over three days.4. Transfer the gel into the supercritical drying chamber, and fill the chamber with methanol.5. Add liquid CO2, then open the chamber's bottom valve to remove the methanol. Make sure the gels are always covered with liquid CO2.6. Wait a day for methanol to diffuse into the liquid CO2.7. Open the bottom valve and remove more methanol.8. Repeat the methanol draining procedure while making sure the gels stay submerged in liquid CO2. Repeat the CO2 draining/exchange a couple times over 2-3 days.9. Raise the chamber temperature to cause the CO2 to become supercritical. Slowly vent the chamber while applying heat to ensure the CO2 moves from the supercritical phase to the gas phase. Continue venting the chamber slowly, then remove the finished aerogels.

jstults, most chemical supply houses will not sell anything to individuals -- regardless of the hazardous nature of the chemical in question. An accident or misuse of the chemical would result in bad PR and lawsuits, so company executives decided that it is more profitable to forgo the money made from individuals to avoid the risks. This is bad news for home scientists, and it's unlikely to change. The best hope we have is that hackerspaces become well-known enough to order chemicals for their members. I suspect many hackerspaces would currently have trouble ordering from a company like Sigma Aldrich.

Great work on your aerogels, and your documentation. There are a few tricks you can try to reduce your cracking:

1. Fill your dryer all the way full with MeOH prior to pressurization. You'll want to make sure the gels are under liquid when you pressurize.

2. Only drain out a percentage of your pressurized MeOH at first (20-30% at a time) with breaks in between before you exchange pure CO2. The co-mingling of the different solvents actually creates a pressure differential within the gel as the pure MeOH tries to escape. This is the biggest "mystery" source of cracking.

3. Contrary to intuition, thermal expansion seems NOT to be the source of the cracks formed in aerogels. Rather, the speed of pressurization and depressurization is much more important, as well slowing the initial MeOH/CO2 exchange as described above.

Awesome work. This stuff has been on my "one of these days" projects list for ages (next to YBCO).

Incidentally, I'm impressed that you successfully obtained physical product from Sigma-Aldrich (however you did it). They seem to have the strongest anti-DIY leanings of any supplier I've ever attempted to deal with.I know of someone who actually had an S-A rep call up to deliver a stern reprimand and a safety lecture in response to an attempted order. The guy is a nuclear engineer.

Have you considered chemically drying the methanol in situ? This will increase the reaction rate due to le chatelier's principal (less water in the methanol). Furthermore, you can avoid changing out MeOH the solution so frequently.

You can use 3A molecular sieves for this task. When they're water logged, recharge them in the oven. It should be cheaper in the long run.

I knew a guy a couple of years ago who minored in chemistry in college (in addition to his EE degree) and did home chemistry as a hobby and was always doing cool stuff in his garage. I think he ended up setting up an LLC to run his chemical purchases through. He said he still had some trouble from time to time because it wasn't a 'real' company, but it was much easier than buying as an individual.

Great project and video! Have been wanting to try this out myself for a decade now, luckily others seem to get things done faster...

Anyway, about the methanol. Have you checked your local RC fuel dealer? Here (Finland) pure methanol for that purpose is about $10 per gallon, which is nowhere near the industrial dirt cheap price, but low enough to become unimportant in a project like this.

The general (un)availability of hobby chemicals to individuals was one of the factors that tipped the scales in favor of a university career for me. Sigma Aldrich is my best friend now. :-)

I would like to ask you where, and at what price,did you get the artificial sapphire window requiredfor the supercritical chamber.I have seen in another video of Nottingam Universitythat a bigger window costs somthing like 3000 pounds Sterlinghttp://www.youtube.com/watch?v=yBRdBrnIlTQI can't find the right video but is surely oneof the three channels that Nottingam Universityhas on youtube.

Anonymous, I did not use sapphire windows. The glass window in my steel chamber came from McMaster (it is a high-pressure, plain "sight glass"). My plastic chamber is built from 1.25" thick acrylic which I also bought from mcmaster.com.

At the step before super-critical drying, you mentioned that the structure pulls tightly together (strong intermolecular bonds?) if left to dry out on the table... I'm wondering if there are any good uses for "zero gel". Is this material very brittle and what the harness factor is. I am very interested in a super dense material.

h0wkeye, the stuff ends up like "silica gel" -- the little beads in those desiccant packets that say "do not eat". It's much more dense than aerogel, but certainly less than any metal and probably most polymers, so it wouldn't qualify as super dense. Tungsten is probably the most economical super dense material, and it also has very high hardness and high-temperature stability.

Hi Ben, I look around on the internet and I couldn't find anything on inter or intra molecular forces of aerogel! This is for an assignment, i've spent about an hour looking for something but i've seen nothing of use except your youtube video.So I was just wondering if you could point me in the right direction in regards to Inter and Intra Molecular forces of Aerogel that is dried with carbon dioxide? thank you so much for your time in advance :)

Rajvignesh, silica aerogel is just pure SiO2, and has all of the same bonds that normal dense SiO2 has, but the structure is expanded with lots of pores and space between the atoms. I'm pretty sure everything that you find regarding bonds in bulk SiO2 would apply to aerogel. There are a lot of different kinds of aerogel, though.

how long do you take to actually complete the aerogel....please respond as soon as possible..because im intending to make one for my final year project...and i only got 7 weeks to complete the project...is 7 weeks enough to complete the aerogels

Perhaps heat stripping or induction heating the unit when processing the phase change rather than a torch along with as you said rearranging the fill nozzle in the manifold may further prevent crazing and cracking.

Hican you help me. I am making aerogel from teos. I am looking from the aerogel.org. but jel didnt occur. teos process is same with aerogel.org ıjust I used ammonium chloride instead ammonium floride. Because I didnt find Ammonium floride. can you give me detail info thanks.